About metadata schema modules

A metadata schema module should implement the following hooks:

hook_xc_schema

It gives an abstract metadata schema, which is converted to MySQL tables and processing rules. The automatic conversion is processed by the XC Metadata module.

The schema should have the following structure:

entity
  title
  description
  fields
    'field name' with the following properties: name, namespace, title, 
         description, required, size, max_size, default_value, possible_values
     attributes
       'attribute name' with the following properties: name, namespace, title, 
         description, required, size, max_size, default_value, possible_values
  namespaces
    'prefix' with the following descriptions: uri, title, description

The schema will be preserved as a row of MySQL table records by the Metadata module's xc_install_schema function.

The entities became XCMetadataEntity objects (MySQL: xc_metadata_entity).

The fields became XCMetadataField objects (MySQL: xc_metadata_field).

The attributes became XCMetadataAttribute objects (MySQL: xc_metadata_attribute).

The namespaces became XCMetadataNamespace objects (MySQL: xc_metadata_namespace).

Above the listed fields every object has a module attribute. The set_definition() method saves the objects into MySQL records.

hook_xc_build

Construct objects from a schema in raw XML format.

• Parsing the raw input for entity instances
• Constructing XCEntity objects
• Calling hook_build_xc() (recursively) for each object

hook_xc_transform(&$object, $format, $params = array())

Convert each XCEntity objects metadata into XC schema in XML format. Returns
an array of XML strings.
Parameters:

$object

Array of XCEntity objects

$format

For export, must equal 'xc:xml'

$params

Additional arguments

hook_xc_format

Gives information about the implemented formats. The hook should return an array of formats. Each format should give information about the following:

name

The name of the format

description

Format description

entities (array)

Array of entity names inside the format

module

The module implements this schema

help

Additional information (help message).

download (boolean)

Is downloadable?

upload (boolean)

Can be uploaded?

file extension

Default file extension of the format (like 'xml')

content type

The MIME content type (like 'text/xml')

namespaceURI

The namespace URI of the root element (like 'http://www.openarchives.org/OAI/2.0/oai_dc')

schemaLocation

The schemaLocations of the referenced namespaces

root element

The XML's root element (like 'oai_dc:dc')

Getting information about schema inside a module - API functions

Getting information about the format

xc_format_get($format_name)

It gives you an array with the following keys:

name

the name of the schema

description

description of the schema

entities

an array of entities name inside the schema

module

the module which defines this schema

help message

download

(boolean) is it possible to download schema record?

upload

(boolean) is it possible to upload schema record?

file extension

the usual file extension (e.g. 'xml')

content type

the mime type of the schema

namespaceURI

the namespace URI of the schema

schemaLocation

the location of XML schemas used inside

root element

the root element's qualified name